Based on the runway and weather reports received en route and just prior to their approach at Peterborough, the flight crew anticipated and planned for a landing on a bare, wet runway. This runway condition would not likely have significantly increased the aircraft landing distance from that of a landing on a bare, dry runway, and the crew would have had sufficient runway to land the aircraft and successfully stop on the runway. The precipitation changed to light snow and rain at about the time the flight crew commenced the approach into Peterborough. A film of slush and water that accumulated on the runway was sufficient to cause hydroplaning but not of sufficient depth to be visible to the crew on approach. The reduced braking action on the wet runway prevented the aircraft from decelerating normally with the anti-skid brake system activated. Despite the fact that an anti-skid brake system would provide a better braking action than a conventional braking system, the captain decided to switch off the anti-skid braking system. When the anti-skid system was deactivated, the wheels locked in a skid, the hydroplaning reduced the braking action to near nil, and the aircraft travelled off the end of the runway. The crew deployed the aircraft drag chute but, for undetermined reasons, the aircraft drag chute did not remain attached to the aircraft to help achieve a shorter landing distance.Analysis Based on the runway and weather reports received en route and just prior to their approach at Peterborough, the flight crew anticipated and planned for a landing on a bare, wet runway. This runway condition would not likely have significantly increased the aircraft landing distance from that of a landing on a bare, dry runway, and the crew would have had sufficient runway to land the aircraft and successfully stop on the runway. The precipitation changed to light snow and rain at about the time the flight crew commenced the approach into Peterborough. A film of slush and water that accumulated on the runway was sufficient to cause hydroplaning but not of sufficient depth to be visible to the crew on approach. The reduced braking action on the wet runway prevented the aircraft from decelerating normally with the anti-skid brake system activated. Despite the fact that an anti-skid brake system would provide a better braking action than a conventional braking system, the captain decided to switch off the anti-skid braking system. When the anti-skid system was deactivated, the wheels locked in a skid, the hydroplaning reduced the braking action to near nil, and the aircraft travelled off the end of the runway. The crew deployed the aircraft drag chute but, for undetermined reasons, the aircraft drag chute did not remain attached to the aircraft to help achieve a shorter landing distance. Precipitation changed from light rain to snow and rain at or near the time at which the flight crew commenced their approach to the airport. The runway surface was contaminated with a thin layer of slush at the time the aircraft landed. The aircraft main landing gear tires hydroplaned on landing roll, reducing the aircraft braking action. The aircraft main landing gear wheels locked in a skid when braking was applied with the brake anti-skid system deactivated. The drag chute, when deployed , did not remain attached to the aircraft. The aircraft overran the end of the runway.Findings Precipitation changed from light rain to snow and rain at or near the time at which the flight crew commenced their approach to the airport. The runway surface was contaminated with a thin layer of slush at the time the aircraft landed. The aircraft main landing gear tires hydroplaned on landing roll, reducing the aircraft braking action. The aircraft main landing gear wheels locked in a skid when braking was applied with the brake anti-skid system deactivated. The drag chute, when deployed , did not remain attached to the aircraft. The aircraft overran the end of the runway. The aircraft hydroplaned and overran the runway, probably as a result of the anti-skid brake system being selected off and maximum brakes being applied. It was not determined whether having the anti-skid system selected would have prevented the overrun, but the distance to a full stop would have been reduced. Contributing to this occurrence was the lack of aerodynamic braking, a result of the drag chute becoming detached.Causes and Contributing Factors The aircraft hydroplaned and overran the runway, probably as a result of the anti-skid brake system being selected off and maximum brakes being applied. It was not determined whether having the anti-skid system selected would have prevented the overrun, but the distance to a full stop would have been reduced. Contributing to this occurrence was the lack of aerodynamic braking, a result of the drag chute becoming detached.